Another class of chemotherapeutics that are specific for the M phase of the cell cycle is the Taxanes. The taxanes include paclitaxel and docetaxel. They bind with high affinity to the microtubules and inhibit their normal function. This class of drugs has a broad range of clinical activity including breast cancer, lung cancer, head and neck cancer, ovarian cancer, bladder cancer, esophageal cancer, gastric cancer and prostate cancer. The most common side effect of these drugs is the lowering of the blood counts. These compounds were first isolated from the bark of the Pacific yew tree Taxus brevifolia in 1963. It was not until 1971 that paclitaxel was identified as the active component and 1993 before it was available for use.